CobaltMVC and Custom Selectors

CobaltMVC supports a variety of CSS selectors including pseudo and attribute matching. To keep things flexible, I've made it so that you can create or overwrite anything built-in. This post we discuss how to create your own for your project.

Right now, if you wanted to select all of the even rows in a table then you could use the pseudo selector...

this.Find("table > :even");

Cool, but what if we wanted to create our own? Here is an example of a selector that finds 'numeric' HTML elements.

//called once to add it to the project
CobaltManagement.RegisterCustomPseudoSelector(
    "numeric", //the name of the selector :numeric
    (nodes, argument) => { //the comparison to use
        decimal container = 0;
        return nodes.Where(node => decimal.TryParse(node.InnerText.Trim(), out container));
    });

//then used from our pages like...
this.Find(":numeric");

You'll notice there are two arguments for the method you provide - First is a list of the available nodes to compare against. The second is an optional 'argument' string. The method should return a list of nodes that should be kept in the selection.

And the argument? That is an optional value in case you want it included in your selector. A good example of using the argument is the nth pseudo selector which returns every x number item.

//Everything within the parens is included as part of the argument
this.Find(":nth(4)");

Note: The argument is passed as a string so you'll need to perform any parsing before you begin using the value.

Attribute selectors match against the attributes of the HTML elements. CobaltMVC checks the values and makes sure that two string are passed (even if they are empty), but any additional parsing needs to be done as part of the method.

That said, the method you use to perform the comparison is slightly different.

CobaltManagement.RegisterCustomAttributeSelector(
    "%", //the prefix to use for the selector @attr%='value'
    (argument, value) => argument.Equals(value, StringComparison.Ordinal)); //the comparison

The special character is what you want to prefix the attribute selector with (if you plan to override the default = selector then you just pass in an empty string). This needs to be a special character so not to be confused with the name of the attribute.

The comparison method itself is just a pair of strings, the first being the argument provided by the user and the second being the value found on the attribute. If the element doesn't have the matching attribute then it is skipped entirely.

So, we could use the method we created in the example above by using...

this.Find("[@title%='Hugoware']");

Pretty neat!